ΔE 17.9, loose: different enough that you should pick on purpose. Sparkling Amethyst is a little darker, much more saturated than Runefang Steel.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Sparkling Amethyst is a little darker, much more saturated than Runefang Steel.
The same difference applies the other way round: Runefang Steel is a little lighter, much more muted.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Runefang Steel on the colour wheel See Sparkling Amethyst on the colour wheel
All matches: Runefang Steel equivalents · Sparkling Amethyst equivalents